The present invention is directed to ducts and duct liners and to a method of forming ducts and duct liners from rigid and semi-rigid insulation boards wherein the configuration of the kerfs formed in the insulation boards as well as the depths, widths and spacing of the kerfs in the insulation boards, control the flexibility of the insulation boards and the structural compression characteristics of the kerf sidewalls or shoulders to facilitate the formation of ducts and duct liners of desired diameters from the insulation boards.
Heating, ventilating and air conditioning systems, exhaust systems and other similar gas flow systems found in large building structures, such as, but not limited to convention centers, sports domes, warehouses, factories and the like require large diameter, high capacity, insulated round or flat oval air ducts for conveying conditioned air from air conditioning units to locations throughout the building structure and for returning air to the air conditioning units for heating or cooling and recirculation or for conveying other gases such as exhaust gases. These large diameter, insulated round or flat oval air ducts typically range from about twenty inches to over one hundred inches in diameter.
Presently, the most commonly used ducts for such large, high capacity, air and gas flow systems are double wall insulated metal ducts. These large diameter, high capacity, metal ducts for conveying air and other gases comprise an outer tubular metal shell, an inner perforated tubular metal shell and one or more layers of glass fiber insulation blankets or other insulation materials intermediate the outer tubular shell and the inner tubular shell. These ducts normally have either a round or a flat oval transverse cross section. Due to their construction which, in essence, comprises a first tubular metal duct contained within a second tubular metal duct, and the labor required to both assemble the first metal duct within the second metal duct and insulate the space between the ducts while maintaining the ducts concentric with respect to each other, these double wall, insulated metal ducts for conveying gases, such as conditioned air, return air, exhaust gases and the like, are relatively expensive.
A second duct, currently in use for conveying gases, comprises a round, tubular metal shell internally lined with a round tubular, preformed, self-supporting, molded, glass fiber insulation sold by Schuller International Inc., under the trademark "SPIRACOUSTIC". This duct system exhibits good thermal and acoustical insulating properties and eliminates the need for a costly perforated metal liner. However, because of manufacturing restrictions relating to the molding of the glass fiber insulation into its tubular shape, this duct system has been size restricted for use with tubular metal shells having internal diameters of twenty-six inches or less.
Thus, although the molded glass fiber insulation liners provide a cost effective lining system with good performance characteristics for tubular metal ducts having internal diameters of twenty-six inches or less, there has been a need to provide large diameter air and gas handling ducts with an insulated lining system other than the costly perforated metal lining system discussed above.